Hello Dan,

you wrote:


The filter we currently have, for which I can't find replacement filter
cartridges anymore,...

I have a similar problem. I solved it by cutting the right piece of filter
material out of a filter from an other manufacturer.


A circulation of 55 gal/hour seems very slow, but maybe it is fine, too.

It also brings some O2 in the water if the surface of the waster is a bit
moving and doesn't brings too much CO2 out.
The other advantage, in my opinion is that a throttled down filter won't let
algues growth as an throttled up one.


greetings


Christoph